1. Field of the Invention
The present invention relates generally to endoscopic surgical instruments. More particularly, the invention relates to a process of manufacturing endoscopic end effectors having a combination of conductive and non-conductive materials, end effectors made by the process, and an endoscopic surgical instrument incorporating the end effectors made by the process. The invention has particular use with respect to bipolar endoscopic cautery. For purposes herein, the term "endoscopic instruments" is to be understood in its broadest sense to include laparoscopic, arthroscopic, and neurological instruments, as well as instruments which are inserted through an endoscope.
2. State of the Art
Endoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, endoscopic/laparoscopic surgery involves one or more incisions made by trocars where trocar tubes are left in place so that endoscopic surgical tools may be inserted through the tubes. A camera, magnifying lens, or other optical instrument is often inserted through one trocar tube, while a cutter, dissector, or other surgical instrument is inserted through the same or another trocar tube for purposes of manipulating and/or cutting the internal organ. Sometimes it is desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organ or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon via the optical instrument in place in the trocar tube.
Various types of endoscopic surgical instruments are known in the art. These instruments generally comprise a slender tube containing a push rod which is axially movable within the tube by means of a handle or trigger-like actuating means. An end effector is provided at the distal end of the tube and is coupled to the push rod by means of a clevis so that axial movement of the push rod is translated to rotational or pivotal movement of the end effector. End effectors may take the form of scissors, grippers, cutting jaws, forceps, and the like. Because of their very small size and the requirements of strength and/or sharpness, end effectors are difficult to manufacture and are typically formed of forged stainless steel. As such, they form an expensive portion of the endoscopic instrument.
Modern endoscopic procedures often involve the use of electrocautery, as the control of bleeding by coagulation during surgery is critical both in terms of limiting loss of blood and in permitting a clear viewing of the surgical site. As used herein, cautery, electrocautery, and coagulation are used interchangeably. Several types of electrocautery devices for use in endoscopic surgery are described in the prior art. Monopolar electrosurgical instruments employ the instrument as an electrode, with a large electrode plate beneath and in contact with the patient serving as the second electrode. High frequency voltage spikes are passed through the instrument to the electrode (i.e., end effector) of the endoscopic instrument to cause an arcing between the instrument and the proximate tissue of the patient. The current thereby generated continues through the patient to the large electrode plate beneath the patient. Monopolar cautery has the disadvantage that the current flows completely through the patient. Because control of the current path through the body is not possible, damage can occur to tissue both near and at some distance from the surgical site. In addition, it is has been observed that monopolar cautery can result in excessive tissue damage due to the arcing between the end effector and the tissue.
In order to overcome the problems associated with monopolar cautery instruments, bipolar instruments have been introduced. In bipolar electrosurgical instruments, two electrodes which are closely spaced together are utilized to contact the tissue. Typically, one end effector acts as the first electrode, and the other end effector acts as the second electrode, with the end effectors being electrically isolated from each other and each having a separate current path back through to the handle of the instrument. Thus, in a bipolar instrument, the current flow is from one end effector electrode, through the tissue to be cauterized, to the other end effector electrode.
Co-owned U.S. Pat. Ser. No. 08/429,596 describes a pair of scissor blades for a bipolar cauterizing surgical scissors which provide the smooth operation and feel of a metal on metal cutting/shearing action. The scissor blades are comprised of an electrically conductive electrode, an electrically insulating material, and a coating of titanium dioxide, chromium dioxide, or zirconium dioxide. The electrode layer is a metal blade which is typically constructed from stainless steel, while the insulating layer is an alumina ceramic which is deposited, bonded, or otherwise fixed on the metal blade, and a titanium dioxide coating is deposited, bonded, or otherwise fixed onto the ceramic and provides the cutting edge and shearing surface. The alumina and titanium dioxide are preferably deposited on a metal scissor blade by thermal spraying of powder at high temperature and standard atmospheric pressure. The titanium dioxide is lubricous and gives the scissor blades the operational feel of metal blades.
In thermal spraying, such as by a high velocity oxygen fuel (HVOF) system, micron sized powder (granules) of the ceramic is sprinkled into the combustion chamber of a rocket-type engine and is sprayed out of the chamber onto a desired substrate. An important factor determining the quality of adhesion of the coating to the substrate is the texture of the substrate surface which the granules strike. The thermal spraying process is enhanced by a roughened substrate surface which aids in the adhesion of the coating to the metal substrate. This is because the granules, in the thermal spraying process, are given thermal and kinetic energy. A smooth surface results in poor adhesion as the granules "bounce" off the surface. In fact, even those granules which adhere to the smooth surface form a poor bond, and peeling or separation of the ceramic form the metal can easily result. However, a roughened metal surface provides a mechanical means for the ceramic powder to bond to the metal substrate and results in better adhesion of the ceramic coating.
In preparation of applying ceramic coatings by the HVOF or similar plasma thermal spray process, it is common to gritblast or sandblast metal substrates to roughen the surfaces (the terms "gritblasting" and "sandblasting" being herein used interchangeably). Gritblasting provides the surfaces with the requisite roughness needed for a proper adhesion of the ceramic granules onto the substrate. However, gritblasting the blades adds an extra step to the blade coating process, is difficult to control, and, as a result, increases the manufacture time and manufacture cost for the blades.